Sometimes font files are saved with the wrong embedding mode which will lead in Internet Explorer to following messag ein browser console: "CSS3114: @font-face failed OpenType embedding permission check. Permission must be Installable." and failing to load the font file. Just run this function below on your .ttf/.woff files which are listed in b…

Change filemode of woff or ttf files

<?php
function convertRestrictedFont($filename) {
	$font = fopen($filename,'r+');
	if ($font === false) {
		throw new Exception('Could not open font file.');
	}

	fseek($font, 12, 0);

	while (!feof($font)) {
		$type = '';
		for ($i = 0; $i < 4; $i++) {
			$type .= fgetc($font);
			if (feof($font)) {
				fclose($font);
				throw new Exception('Could not read the table definitions of the font.');
			}
		}
		if ($type == 'OS/2') {
			// Save the location of the table definition
			// containing the checksum and pointer to the data
			$os2TableDefinition = ftell($font);
			$checksum = 0;

			for ($i = 0; $i < 4; $i++) {
				fgetc($font);
				if (feof($font)) {
					fclose($font);
					throw new Exception('Could not read the OS/2 table header of the font.');
				}
			}

			// Get the pointer to the OS/2 table data
			$os2TablePointer = ord(fgetc($font)) << 24;
			$os2TablePointer |= ord(fgetc($font)) << 16;
			$os2TablePointer |= ord(fgetc($font)) << 8;
			$os2TablePointer |= ord(fgetc($font));

			$length = ord(fgetc($font)) << 24;
			$length |= ord(fgetc($font)) << 16;
			$length |= ord(fgetc($font)) << 8;
			$length |= ord(fgetc($font));

			if (fseek($font, $os2TablePointer + 8, 0) !== 0) {
				fclose($font);
				throw new Exception('Could not read the embeddable type of the font.');
			}

			// Read the fsType before overriding it
			$fsType = ord(fgetc($font)) << 8;
			$fsType |= ord(fgetc($font));

			error_log('Installable Embedding: ' . ($fsType == 0));
			error_log('Reserved: ' . ($fsType & 1));
			error_log('Restricted License: ' . ($fsType & 2));
			error_log('Preview & Print: ' . ($fsType & 4));
			error_log('Editable Embedding: ' . ($fsType & 8));
			error_log('Reserved: ' . ($fsType & 16));
			error_log('Reserved: ' . ($fsType & 32));
			error_log('Reserved: ' . ($fsType & 64));
			error_log('Reserved: ' . ($fsType & 128));
			error_log('No subsetting: ' . ($fsType & 256));
			error_log('Bitmap embedding only: ' . ($fsType & 512));
			error_log('Reserved: ' . ($fsType & 1024));
			error_log('Reserved: ' . ($fsType & 2048));
			error_log('Reserved: ' . ($fsType & 4096));
			error_log('Reserved: ' . ($fsType & 8192));
			error_log('Reserved: ' . ($fsType & 16384));
			error_log('Reserved: ' . ($fsType & 32768));

			fseek($font, ftell($font) - 2);

			// Set the two bytes of fsType to 0
			fputs($font, chr(0), 1);
			fputs($font, chr(0), 1);

			// Go to the beginning of the OS/2 table data
			fseek($font, $os2TablePointer, 0);

			// Generate a new checksum based on the changed
			for ($i = 0; $i < $length; $i++) {
				$checksum += ord(fgetc($font));
			}
			fseek($font, $os2TableDefinition, 0);
			fputs($font, chr($checksum >> 24), 1);
			fputs($font, chr(255 & ($checksum >> 16)), 1);
			fputs($font, chr(255 & ($checksum >> 8)), 1);
			fputs($font, chr(255 & $checksum), 1);

			fclose($font);

			return true;
		}
		for ($i = 0; $i < 12; $i++) {
			fgetc($font);
			if (feof($font)) {
				fclose($font);
				throw new Exception('Could not skip a table definition of the font.');
			}
		}
	}

	fclose($font);

	return false;
}